To to OP.
If you bought it and its paid for, you might want to drive it till it drops. IMO, no other vehicle comes close to the D in performance/FE/price.
When you retire, you only need to fill your tank maybe once a month as you drive less.
Also you may want to take more road trips so the D is still the perfect vehicle.

I'm almost in the same boat as you. I'm 63 this year but have no plans to retire from my business.
I paid for my D in full when I bought it in Nov 2009. This is the first vehicle I've driven for 3 years. All other vehicles lasted not more than 2. With the D I am still enjoying it as much as the day I got it and I can't think of another vehicle that can replace it for now unless BMW brings in the f10d or f30d touring.
But it's nice not to have any lease/loan payments and just enjoy the D.